randomsequential

Randomsequential is an abbreviation commonly used to refer to the Random Sequential Adsorption (RSA) process, a stochastic method for generating dense packings of particles on a substrate. In the RSA protocol, particles are introduced one after another at random positions and orientations, and each placement is accepted only if it does not overlap with particles already adsorbed. Accepted particles are permanently fixed (the “sequential” nature), and the procedure continues until no further non-overlapping placements are possible, creating an irreversible jammed state.

The RSA model was first introduced in the early 1970s to study monolayer deposition of elongated molecules and later applied to a wide range of systems, including colloidal suspensions, polymer adsorption, and nanostructure assembly. It captures essential features of irreversible surface processes, such as the development of spatial correlations and the non-equilibrium nature of the final configuration. Theoretical analyses of RSA typically compute the jamming coverage, i.e., the fraction of substrate area occupied at saturation, which depends on particle shape, dimensionality, and dimensional constraints of the substrate.

Computational implementations of RSA involve random number generation for position and orientation, geometric overlap tests, and termination criteria that may be based on a fixed number of attempted insertions. Variations of the basic RSA scheme have been devised, such as time-dependent RSA, where particle arrival follows a Poisson process, and generalized RSA, which allows limited desorption or reshuffling. Despite its simplicity, RSA remains a benchmark model for studying heterogeneous nucleation, glassy dynamics, and other kinetically constrained systems.